Surgical stitching instruments have been widely used in surgical operations for stitching up wounds, and stitching up and cutting interior tissues. U.S. Pat. No. 5,129,570 discloses a typical surgical stitching instrument which is provided with double functions of stitching and cutting. That is to say, the surgical stitching instrument is capable of stitching up wounds and simultaneously cutting spilth tissues. Such surgical stitching instruments usually include a pair of top and bottom forceps, a closing handle for closing the top and bottom forceps, an anvil and a staple cartridge respectively mounted on opposite far ends of the top and bottom forceps, a staple-pushing rod, a staple-pushing piece and a cutter all moveably mounted in the staple cartridge, and a push button for moveably pushing the staple-pushing piece and the cutter. The staple cartridge includes inside stitch nails which are pushed by the staple-pushing piece to move towards the anvil. The tissues between the staple cartridge and the anvil are cut off by the cutter.
Error firing action means that after the instrument has been fired, it refires without any nails in the reloading unit. The consequence of such error firing action will extrude the nails which have already well closed and will cause over-deformation of the nails. As a result, the wound closure cannot be good enough, and serious medical malpractices and sequelae sometimes occur.
In order to avoid this kind of phenomenon, the conventional surgical stitching instruments usually have safety mechanisms for error firing protection.
U.S. Pat. No. 5,129,570 discloses such a safety mechanism which includes a middle safety block having a cutter channel and a staple-pushing rod channel, and an elastic piece mounted below the cutter. When the instrument is at an open position, which means the top and bottom forceps are not closed, the cutter are upsprung by the elastic piece so that the cutter cannot pass the cutter channel. When the instrument is loaded with the staple cartridge, a transverse lever which is pivotally mounted on top of the staple cartridge presses against a top portion of the cutter. The cutter overcomes the elasticity of the elastic piece and recovers to a position where the cutter can pass through the cutter channel. As a result, under this condition, the instrument can be used in firing. When the instrument is completely fired, the cutter is pulled back to the original position. Under this condition, the transverse lever has been pivoted to a position where the transverse lever cannot press the top portion of the cutter anymore. The cutter is upsprung again by the elastic piece so that the cutter cannot pass the cutter channel and thereby preventing error firing.
U.S. Pat. No. 7,055,730 discloses another safety mechanism which includes a protection cover mounted on the cutter. The protection cover is connected to the staple cartridge through a pin and the protection cover is rotatable with respect to the pin under the function of a torsional spring. The protection cover is mateable with and connected to the cutter before firing of the instrument for not only protecting the blade, but also keeping horizon for closing the instrument. When the instrument is completely fired, the cutter returns back to the original position. Under this condition, the protection cover breaks away from the cutter, once the instrument is opened, the protection cover overturns immediately under the function of the torsional spring. The protection cover is ultimately and vertically located between the anvil and the staple cartridge which results in the instrument unclosed, thereby avoiding the error firing possibility of the instrument. However, in fact, such safety mechanism cannot absolutely avoid empty firing of the instrument between the time after the firing of the instrument is complete and before the instrument is opened. Therefore, the conventional second error firing protection cannot continue the entire process between the time when the firing of the instrument is complete and before a new staple cartridge is installed. Thus, certain operation risk still exists.